1. Field of the Invention
This invention relates generally to compositions, methods and apparatus used for use in the manufacture of semiconductor, photovoltaic, LCF-TFT, or flat panel type devices.
2. Background of the Invention
During the fabrication of a transistor, silicide layers may be used to improve the conductivity of polysilicon. For instance nickel silicide (NiSi) may be used as a contact in the source and drain of the transistor to improve conductivity. The process to form metal silicide begins by the deposition of a thin transition metal layer, nickel for instance, on the polysilicon. The metal and a portion of the polysilicon are then alloyed together to form the metal silicide layer.
Chemical Vapor Deposition (CVD) and Atomic Layer Deposition (ALD) are the main gas phase chemical process used to control deposition at the atomic scale and create extremely thin coatings. In a typical CVD process, the wafer is exposed to one or more volatile precursors, which react and/or decompose on the substrate surface to produce the desired deposit. ALD process are based on sequential and saturating surface reactions of alternatively applied metal precursor, separated by inert gas purging.
In order to get high-purity, thin and high-performance solid materials on the wafer, metal precursors with high purity, high thermal stability, and high volatility are required. Furthermore, they should vaporize rapidly and at a reproducible rate, a condition which is more easily achieved for liquid precursors, than it is for solid precursors.
Some amidinate transition metal precursors are and have been successfully used for deposition by ALD. Although volatile, those precursors are usually solids with high melting point (>70° C.) and can suffer some time from thermal instability (nickel for instance), which is a drawback for the ALD process. On the other hand, bis-cyclopentadienyl precursors are known to be liquid or low melting point solid, and still volatile depending on the substitution on the cyclopentadienyl. For instance, Ni(Me-Cp)2: solid mp=34-36° C., Ni(Et-Cp)2: liquid, Ni(iPr-Cp)2: liquid. However bis-cyclopentadienyl precursors still suffer from thermal instability, with nickel for instance.
Consequently there exists a need for new transition metal precursors suitable for CVD or ALD process.